Meteor Scatter



by Joel KQ0J
I have recently enjoyed some 6 meter meteor scatter contacts on a budget
using the new version of WSJT-X software with the new MSK144 mode. I am
just using a homebrew 6M square loop – omnidirectional antenna. I am just
using A 100w RIG, running 50-70W output on the 15 second bursts that the
software transmits with.

A good calling frequency is 50.280. People also use 285, 287, 290 when
arranging contacts. WSJT-X V1.7 allows a station to state ” CQ 285 W2FRD”
when calling CQ on 280 and when you click your mouse on that decode, the
SW will QSY automatically for you to 285 when you click on that station!

During the recent Geminids meteor shower on Dec 13-15, I made 2 confirmed
meteor scatter contacts and a handful of partial contacts. I am sure I could
do better on the next shower. Seems most ops are on during the early morning
till about 9 AM. I was only on for an hour or two during the last shower but
it was enough time to see how well this software works.

There is a website where you can online chat with other currently active
stations, set up QSOs and see who is listening or transmitting on what
frequency and mode. http://www.pingjockey.net/cgi-bin/pingtalk

Download the Beta WSJT-X software V 1.7 at: https://sourceforge.net/projects/wsjt/

Descriptive text from: http://physics.princeton.edu/pulsar/k1jt/v1.7_Features.txt

New Mode for meteor scatter:
1. MSK144 is intended for meteor scatter at 50 MHz and higher. It
uses a low-density parity check code (LDPC) designed by Steve Franke,
K9AN. The mode is a direct descendant of the now-defunct mode JTMSK,
with a number of improvements for better performance on weak and short
meteor pings. The effective character transmission rate is about 250
cps, compared with 147 cps for FSK441. Like JT4, JT9, JT65, and
QRA64, MSK144 uses strong forward error correction. Message decoding
is all or nothing: partial decodes do not occur, and you will see
little or no garbage on your screen.

Standard MSK144 message frames are 72 ms long, compared with about 120
ms for an equivalent FSK441 message. The MSK144 waveform allows
coherent demodulation, allowing up to 3 dB better sensitivity. After
QSO partners have exchanged callsigns, MSK144 can use even shorter
messages, only 20 ms long. As in all the fast modes in WSJT-X, the 72
ms (or 20 ms) messages are repeated without gaps for the duration of a
transmission cycle. For most purposes we recommend a T/R cycle
duration of 15 s, but 5 s and 10 s sequences are also supported.

Short (“Sh”) messages in MSK144 are intended primarily for 144 MHz and
higher frequencies, where most pings are very short. These messages
do not contain full callsigns; instead, they contain a hash of the two
callsigns along with a report, acknowledgement, or 73. Short messages
are fully decodable only by the station to whom they are addressed, as
part of an ongoing QSO, because only then will the received hash match
that calculated using the known strings for “My Call” and “DX Call”.
If you are monitoring someone else’s QSO, you will not be able to
decode its Sh messages.

An MSK144 signal occupies the full bandwidth of a typical SSB
transmitter, so transmissions are always centered at an offset of
1500Hz. For best results, selectable or adjustable Rx and Tx filters
should be set to provide the flattest possible response over at least
300 – 2700 Hz. The maximum permissible frequency offset between you
and your QSO partner is 200 Hz, and less is better.

Gretna, NE